The present invention relates to elongated structural members such as pilings, poles and columns, and methods for making such members.
Concrete, steel, and wood are conventionally used for pilings, telephone poles, and the like. However, each of these materials has disadvantages. Concrete and steel pilings are heavy and awkward to maneuver. Neither concrete nor steel pilings make good fender pilings because neither is "forgiving" when impacted. Under impact steel bends and buckles and concrete shatters. Both concrete and steel pilings are expensive to repair. -Furthermore, steel, either standing alone or as a reinforcement in porous concrete, is subject to corrosion.
Wood pilings are plagued by wear and tear and are attacked by wood-boring marine organisms. Wood pilings are typically treated with creosote, but even this material can be ineffective against modern marine borers. These marine borers can only be stopped by wrapping the wood pilings in plastic coverings. However, these plastic coverings cannot withstand much wear and tear, especially abrasion from normal vessel contact. So in addition to a thin plastic wrap, wooden fender piles often require thick plastic wrappings, which are expensive to put in place. Wood used for telephone poles is subject attack from environmental hazards such as woodpeckers, and in desert locations, there can be severe erosion from sandstorms.
Composite pilings are also known, being disclosed for example in U.S. Pat. No. 5,180,531 to Borzakian, that document being incorporated herein by this reference. The '531 patent discloses a plastic pipe having an inner pipe core or mandrel being 6 inches or less in diameter, and a substantially homogenous coating being at least two inches thick. The thick plastic coating provides the bulk of the mechanical strength, being formulated with a desired combination of flexibility, brittleness, and impact resistance for use as pilings including fender pilings of docks, telephone poles, light standards, etc. The plastic pipe of the prior art is not entirely satisfactory in that uniform thick coatings that are free of voids are somewhat difficult to achieve, and longer lengths of the pilings such as from 20 feet to 60 feet normally require assembly of shorter length segments, with consequent degradation of structural and environmental integrity and increased cost of fabrication. Also, when the plastic pipe is provided with the homogenous plastic coating having with a desired flexibility and impact resistance for fender piling applications, the bending strength is less than desired for withstanding side loads that are produced by contact with approaching vessels.
U.S. Pat. No. 5,766,711 to Barmakian discloses a composite camel structure including a pipe mandrel and a thermally bonded plastic cushion surrounding the mandrel, that patent being incorporated herein by this reference. A mold having the mandrel centered therein is filled with molten plastic, the plastic being cooled and solidified by feeding water into the mandrel for progressively solidifying the cushion member along mandrel for producing a thermal bond without excessive tensile strain in the plastic material, thereby to achieve a substantially unbroken outside surface. Although the use of cooling water inside the mandrel reduces the likelihood of cracks and voids in the cushion material, the pipe mandrel is undesirably expensive, and pilings having pipe encapsulated in plastic have structural disadvantages as discussed above.
In view of these problems with conventional pilings and telephone poles, there is a need for pilings and telephone poles that have a long life, are easily installed, environmentally sound, durable in use, and having high bending strength.